.RMGB file extensions

I see several notes about this being a "backup" format or some other type of zip file, etc, but I don't see an explanation of how to open a file that has been downloaded with that extension. I am working with a friend who uses Legacy software (among others) & he sent me a fairly large file with this extension. My Windows XP does not recognize this estension, & all of the websites for file extensions refer to ".RMVB", which I don't think I want. I have the free version of RootsMagic, but this doesn't seem to recognize the extension either. Where do I get software that DOES allow me to open or view this type of file? Some queries I've seen also state that RM v4 doesn't display this as well, so I haven't seen a clear answer to this question. Hope someone can explain... Thanks

I see several notes about this being a "backup" format or some other type of zip file, etc, but I don't see an explanation of how to open a file that has been downloaded with that extension. I am working with a friend who uses Legacy software (among others) & he sent me a fairly large file with this extension. My Windows XP does not recognize this estension, & all of the websites for file extensions refer to ".RMVB", which I don't think I want. I have the free version of RootsMagic, but this doesn't seem to recognize the extension either. Where do I get software that DOES allow me to open or view this type of file? Some queries I've seen also state that RM v4 doesn't display this as well, so I haven't seen a clear answer to this question. Hope someone can explain... Thanks

You need to get your friend to send you the file again as a .GED extension (gedcom export), that is the only loose standard for cross platform information exchange.

“The best preparation for tomorrow is doing your best today"

Current user of Rootsmagic version 7.5.5.0, Family Tree Maker 2014 and Legacy 7.5 on Win 10

The rmgb is a RootsMagic backup file.
It is the same as a ZIP file except the extension is different.
If you edit the filename in something like Windows explorer so that the extension is ZIP, you could expand it with a popular decompression program, even Windows, BUT, WHY, do that? you can't see much in the database with any other program anyway.

RootsMagic expands them with the RESTORE command in the File menu and opens them for you so you can use them.
The only problem is that if you Restore the backup, it will overwrite any regular "rmgc" file of the same name as the file you backed up to create that file.
Effectively overwriting the original, ALTHOUGH you do get a warning to that effect.
Of course, you could always restore the backup to a different folder.

It looks as though RM4 will also import Legacy databases directly (as opposed to indirectly via GEDCOM import). That extension is FDB, so if you can receive the information in that format, you should be able to import it.

Within the RootsMagic software, RMGC is the RM4 database file extension, while RMGB is the RM4 backup file extension.

*Edit:
Since you stated, "among others", is it possible that knowing that you used RM4 software and for your convenience, he sent you a backup file from RM4? You want to save/import across different software formats as infrequenly as possible for fear of losing information, so it's important to find out exactly from which software package the file that was sent to you was made. Fortunately, backing up and restoring between RMGC and RMGB will retain all data integrity -- it's the converting between FDB and RMGC (or FDB, GED, and RMGC, etc.) that could potentially be of concern).